This invention relates to new and unique high-area contactors suitable for use in substantially any kind of chemical or biological reaction or process wherein a substrate having a high area is needed. More particularly this invention relates to high-area contactors used in mass transfer operations and catalytic scrubbers. The contactors must also have the ability to withstand the turbulance of a fluid flowing therethrough, vibrations, abrasions and other movements which would tend to destroy or otherwise break a fragile high-area contactor.
As will be recognized by those skilled in the art, many chemical reactions such as that in an automobile catalytic convertor, as well as those which occur in gas/liquid fluid exchange packing towers require a reaction support means having a high surface area. In addition, biological processes such as enzyme reactions which might be used in sewage treatment plants on the conversion of sugars to alcohols by fermentations as well as other processes using enzymes and other biological operatives are facilitated by the use of supports having extremely high contact areas. Such biological processes may also take place in packing towers on alternately may occur in rotary biological contactors. In the past, the high area necessary for these processes has been provided substantially according to two techniques. In the first technique, a monolith member, such as for example a wire mesh, a sponge or the like substantially fills a container in which the desired reaction is to take place. Unfortunately, when such a monolith structure is used for filtering, it will be appreciated that the filter may well tend to clog with particles which are being filtered therefrom by the liquid being passed therethrough. Thus, it will be appreciated that such filters, of course, require continuous cleaning and maintenance. In addition, the use of such meshes, and sponges which are often mde of plastic or wire, cannot be used with extreme high temperatures, as the metal meshes may well tend to react with the fluid passing therethrough and the plastic sponges may simply melt. In this regard, U.S. patent applications No. 937,085 filed by Clyde et al solves the excess heating problem by making packing elements out of a ceramic sponge. Mr. Clyde's U.S. Pat. Nos. 3,900,646 and 3,998,758 described methods of plating the sponge with metals. Unfortunately such ceramic sponge packing materials do suffer from the disability of being quite fragile and subject to breaking and flaking. However, it will be appreciated that these type monolithic sponges and meshes do tend to provide a such greater amount of contact surface than do other techniques.
Also, as is mentioned heretofore such monolithic foam and mesh type support members although providing great surface area for both chemical and biological processes, will tend to clog if the process results in a precipitate. Especially in the case of the biological processes, the growth of the enzymes and microbes will quickly fill the small spaces in these type elements. It is also important to realize that although these wire mesh and sponge type elements are desirable because of their extremely light weight, once they start filling with the biomass and precipitate the weight often increases many fold.
Although it is well known that a large surface area is important in an effective gas contactor, it has also been observed that the coefficient of mass transfer from a gas to a liguid droplet is ten to thirteen times greater than from a gas to a flat surface. Thus, it will be appreciated that the use of a foam type monolith having great numbers of sharp and clearly defined points from which droplets can be produced as well as a large surface area is specially efficient.
Techniques (other than the monolith discussed above) commonly used to provide high surface area supports are the packed column technique and rotary biological contactor. According to these techniques, small individual elements which may have a particle size which ranges from small sand up to three inches in diameter are used. These elements are poured into a container to form a filter bed, distillation column or packed column. It is well understood, of course, by those skilled in the art that although small elements which might be the size of the grain of sand or smaller provide tremendous surface area for a reaction, they also provide very great resistance to the flow of the fluid therethrough. On the other hand larger elements, such as for example two or three inch spheres, although providing less resistance to the flow of the fluid do not offer near the surface area of the smaller particles. The reason that the smaller particles provide such resistance is that these particles tend to pack together such that there is little or no space left between adjacent particles. In the past, when a higher area was desired, it was customary to go to a smaller size but this increases cost and weight and decreases percentage of free space. The cost per cubic foot of 1/2-inch ceramic Raschig rings, for example is nearly four times that of the 2-inch size in large quantities. Further, even where spaces may remain between adjacent particles, precipitates or biological growth may quickly fill these spaces. Still another difficulty, is that the plate or support upon which the filter material or packing material rests must include perforations therethrough which are smaller than the smallest particle size. For example, a bed of sand cannot be supported by a metal plate having perforations therethrough which are greater than the smallest of the grains of sand or the sand would simply sift through the perforations. Thus, it is really appreciated that the base support itself quickly becomes one of the primary causes of resistance of a fluid through such a filter and support member. In the present invention a relatively open support plate can be used with 2-inch rings while a high area provided by the inner sponge which also promotes drop formation, has a high percentage of free space and low weight. In a distillation column, to get high purity it is especially important to have an efficient packing in the top of the column, the so-called "pinch" region of the McCabe-Thiele diagram. Excess weight in the top is a contributing factor in packing breakage in the bottom of the column. Old columns could be upgraded by simply replacing some packing in the top with a more efficient type. Consequently, to provide the desired surface area on elements having a size substantially larger than the perforations in the support plate, packing elements of various sizes and shapes are used. Such packing elements include for example, pierced hollow ceramic spheres such as disclosed in U.S. patent application, Ser. No. 39268 filed by Robert A. Clyde who is the inventor of the present invention, as well as Raschig rings, pall rings, berl saddles and Intalox saddles all of which are available from companies such as the Norton Company of Akron Ohio. The purpose of these various shapes, is of course, to provide a large amount of surface area while at the same time providing shapes that will not pack down and close up the spaces in between each element. As an example, the Norton Company produces a type of element called the Super Intalox Saddle which has a rather intricate design such as shown in the prior art FIG. 1 of the drawings. The purpose of this intricate shape is to help maintain free space in the packing bed by holding the individual pieces in position thereby reducing settling of the bed. The design is also intended to provide more interstital space and transfer points for the liquid which constantly moves across the surfaces to promote greater mass transfer. However, it will be appreciated that although such a shape is effective, the production of great quantities of such intricately shaped elements for purpose of packing a column is also very expensive. It will be appreciated that such elements as the Intalox Saddle and the Raschig ring as well as others are often made of high-impact plastic or ceramics or other hard materials which can withstand abrasion, vibrations turbulent fluid flow and the like without breaking or fracturing.
Thus, it is seen that a choice often must be made between a high-area fragile foam material or individual packing elements with much less contact surface which can withstand abrasion and abuse. There is a third choice, unfortunately it is not much better. That is, the surface area can be increased while at the same time maintaining the high strength characteristics by providing intricate shaped packing elements such as the Super Intalox Saddle. The trade off, being of course, that the Super Intalox Saddles or similar intricate shaped designed individual units are substantially more expensive than the simply shaped spheres, Raschig rings or the foam materials.
As was mentioned heretofore, one of the primary purposes of a high-area contactor is for the purpose of establishing contact between a liquid and a gas or a liquid and a biological operative. One way of accomplishing such high-area contact is by the use of the RBC (rotary biological contactor): Examples of an RBC is discussed in U.S. Pat. Nos. 4,028,244 and 3,956,127 both issued to Leaf Holmberg. According to these patents, there is disclosed a cylindrical shaped container adapted for rotation along its axis, and which is partially submerged in a liquid. The cylindrical container is for example made of wire mesh and is filled with individual items such as the plastic spherical hollow balls described in the patent. Thus, the spherical balls provide a surface for contact between the liquid and the gas or air above the rotating contactor. As the cylinder rotates, the various plastic balls are alternately exposed to the liquid and the air. In addition, column or tower packed contactors such as discussed in U.S. Pat. No. 3,796,657 issued to Pretorius et al provides a tall tower within which is packed individual element. According to this type packed column for mass transfer operations, gas-liquid contact takes place as the liquid which is usually introduced at the top of the column flows down over the packing material contained within the column at the same time the gas introduced at the bottom of the column flows upward through the column countercurrently to the liquid. The purpose of the packing material, of course, is to increase the intimacy of contact between the two fluid phases to facilitate the transfer of material from the gas phase to the liquid phase or vice versa. As was mentioned heretofore, of course, the high contact area may be provided by a porous medium such as a wire mesh or foam or may instead be made of individual elements such as Raschig rings or Intalox Saddles or other individual elements. Since several factors are involved in providing a packing column which operates efficiently, of particular importance is the selection of the packing material. Thus, the packing material should be constructed as was discussed heretofore in such a manner that it provides a minimum pressure drop across the column. Also, of course, it must be chemically inert with respect to the various phases of liquid and gas which it contacts. It should also have high mechanical durability and be able to withstand turbulance abuse and abrasion that might be experienced, while at the same time be light enough so that elements in the bottom of a high column will not break.
As was discussed heretofore, the coefficient of mass transfer of gas to liquid droplets is ten to thirteen times greater than that of a gas to a flat surface. As a result of this higher efficiency, certain packing material such as the Intalox Saddles have been designed to enhance the droplet formation. Thus, from the above, it can be seen that a great deal of time and attention has been paid in the past for purposes of finding a better way of providing a high surface area which has the strength and ability to withstand fracturing and the ability to withstand high temperature while at the same time remaining inert to substantially all possible chemical and biological reactions. For a more complete discussion of the prior art and efforts made with respect to these problems, the reader is again referred to patent application Ser. No. 937,085.